Dispersion and conditioning techniques for thick fine tailings dewatering operations

ABSTRACT

Techniques are described that relate to enhancing flocculation and dewatering of thick fine tailings, for example by reducing process oscillations. One example method includes dispersing a flocculant into thick fine tailings having a turbulent flow regime to produce turbulent flocculating tailings; subjecting the turbulent flocculating tailings to shear to build up flocs and increase yield stress, to produce a flocculated material having a non-turbulent flow regime; and shear conditioning the flocculated material to decrease the yield stress and produce conditioned flocculated tailings within a water release zone; and dewatering the conditioned flocculated tailings, for example by employing sub-aerial deposition. The thick fine tailings may have a Bingham Reynolds Number of at least 40,000 upon flocculant addition. Inhibiting process oscillations may include providing turbulent tailings feed, configuring a downstream pipeline assembly to reduce backpressure fluctuations and/or reducing air content in the flocculant solution, for example.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/408,695, filed Dec. 17, 2014, which is the U.S. national stage ofInternational application No. PCT/CA2013/050491, filed Jun. 21, 2013,which claims the priority of U.S. provisional application No.61/662,709, filed Jun. 21, 2012, the disclosures of which areincorporated in their entireties herein.

FIELD OF THE INVENTION

The present invention generally relates to the dispersion and/orconditioning of thick fine tailings for dewatering operations.

BACKGROUND OF THE INVENTION

Tailings derived from mining operations, such as oil sands mining, areoften placed in dedicated disposal ponds for settling.

The settling of fine solids from the water in tailings ponds is arelatively slow process. Certain techniques have been developed fordewatering fine tailings. Dewatering of thick fine tailings can includecontacting the thick fine tailings with a flocculant and then depositingthe flocculated fine tailings in a deposition area where the depositedmaterial can release water and eventually dry.

There are several factors that may influence the performance ofdewatering operations. For instance, inadequate dispersion of theflocculant into the thick fine tailings can decrease the efficiency ofthe flocculating agent and the overall dewatering. Inadequate mixing mayalso result in inefficient use of the flocculating agents, some of whichremain unmixed and unreacted resulting in higher flocculant doserequirements to achieve optimally dosed conditions.

In the context of dewatering thick fine tailings, there are a number ofchallenges related to flocculant addition and handling of the resultingflocculation mixture.

SUMMARY OF THE INVENTION

Various techniques are described that may be used for enhancingflocculation and dewatering of thick fine tailings.

In some implementations, there is provided a method of treating thickfine tailings, comprising:

-   -   providing an in-line flow of the thick fine tailings;    -   adding a flocculant into the in-line flow of the thick fine        tailings to produce an in-line flow of flocculating tailings        material, wherein the in-line flow of the thick fine tailings        has a turbulent flow regime upon addition of the flocculant;    -   shearing the in-line flow of the flocculating tailings material        to induce floc build-up, increase a yield stress thereof and        reduce turbulence thereof, to thereby produce a non-turbulent        in-line flow of flocculated material;    -   subjecting the in-line flow of the flocculated material to shear        conditioning to decrease the yield stress thereof and produce a        conditioned flocculated tailings material that is within a water        release zone wherein water separates from the conditioned        flocculated tailings material; and    -   dewatering the conditioned flocculated tailings material.

In some implementations, the in-line flow of the thick fine tailings hasa Bingham Reynolds Number of at least 40,000 upon addition of theflocculant.

In some implementations, the in-line flow of the thick fine tailings hasa Bingham Reynolds Number of at least 50,000 upon addition of theflocculant.

In some implementations, the in-line flow of the thick fine tailings hasa Bingham Reynolds Number of at least 60,000 upon addition of theflocculant.

In some implementations, the in-line flow of the thick fine tailings hasa Bingham Reynolds Number of between 40,000 and 65,000 upon addition ofthe flocculant.

In some implementations, the in-line flow of the thick fine tailings hasa Bingham Reynolds Number of between 45,000 and 60,000 upon addition ofthe flocculant.

In some implementations, providing the turbulent flow regime comprisesregulating a feed flow rate of the thick fine tailings above a minimumthreshold.

In some implementations, providing the turbulent flow regime comprisesconfiguring a pipeline assembly that transports the flow of thick finetailings for addition of the flocculant and transports the flocculatingtailings after addition of the flocculant, to have a sufficiently smallpipe diameter.

In some implementations, providing the turbulent flow regime comprisesensuring a sufficiently low viscosity of the in-line flow of the thickfine tailings upon addition of the flocculant.

In some implementations, the non-turbulent in-line flow of flocculatedmaterial has a laminar flow regime.

In some implementations, the in-line flow of the thick fine tailings isprovided by pumping at a substantially constant flow rate.

In some implementations, the in-line flow of the thick fine tailings isprovided by pumping at substantially constant rotations per minute.

In some implementations, the adding of the flocculant comprisesinjecting a solution comprising the flocculant into the in-line flow ofthe thick fine tailings.

In some implementations, the adding of the flocculant is performed byratio control with respect to the in-line flow of the thick finetailings.

In some implementations, the dewatering comprises depositing theconditioned flocculated tailings material onto a sub-aerial depositionsite. In some implementations, the dewatering comprises subjecting theconditioned flocculated tailings material to thickening and/orfiltering.

In some implementations, there is provided a method of dispersing aflocculant into an in-line flow of thick fine tailings, comprising:

-   -   providing the in-line flow of the thick fine tailings with a        turbulent flow regime to provide a turbulent feed;    -   adding the flocculant into the turbulent feed to produce an        in-line turbulent flow of flocculating tailings material;    -   shearing the in-line turbulent flow of the flocculating tailings        material to induce floc build-up, increase a yield stress        thereof and reduce turbulence thereof, to thereby produce a        non-turbulent in-line flow of flocculated material.

In some implementations, the turbulent feed has a Bingham ReynoldsNumber of at least 40,000 upon addition of the flocculant.

In some implementations, the in turbulent feed has a Bingham ReynoldsNumber of at least 50,000 upon addition of the flocculant.

In some implementations, the turbulent feed has a Bingham ReynoldsNumber of at least 60,000 upon addition of the flocculant.

In some implementations, the turbulent feed has a Bingham ReynoldsNumber of between 40,000 and 65,000 upon addition of the flocculant.

In some implementations, the in turbulent feed has a Bingham ReynoldsNumber of between 45,000 and 60,000 upon addition of the flocculant.

In some implementations, providing the turbulent flow regime comprisesregulating a feed flow rate of the thick fine tailings above a minimumthreshold.

In some implementations, providing the turbulent flow regime comprisesconfiguring a pipeline assembly to have a sufficiently small pipediameter, wherein pipeline assembly transports the turbulent feed andthe in-line turbulent flow of flocculating tailings material.

In some implementations, providing the turbulent flow regime comprisesensuring a sufficiently low viscosity of the in-line flow of the thickfine tailings upon addition of the flocculant.

In some implementations, the non-turbulent in-line flow of flocculatedmaterial has a laminar flow regime.

In some implementations, the in-line flow of the thick fine tailings isprovided by pumping at a substantially constant flow rate.

In some implementations, the in-line flow of the thick fine tailings isprovided by pumping at substantially constant rotations per minute.

In some implementations, the adding of the flocculant comprisesinjecting a solution comprising the flocculant into the turbulent feed.

In some implementations, the adding of the flocculant is performed byratio control with respect to the turbulent feed.

In some implementations, the adding of the flocculant comprisesco-annularly injecting a plurality of jets comprising the flocculantinto the turbulent feed.

In some implementations, the jets comprising the flocculant extend intothe turbulent feed co-directionally with the flow direction thereof.

In some implementations, there is provided a system for treating thickfine tailings, comprising:

-   -   a feed pipeline assembly for providing an in-line flow of the        thick fine tailings;    -   a pump for pumping the in-line flow of the thick fine tailings;    -   an in-line addition assembly in fluid communication with the        feed pipeline assembly for adding a flocculant into the in-line        flow of the thick fine tailings to produce an in-line flow of        flocculating tailings material;    -   wherein the pump, the feed pipeline assembly and the in-line        addition assembly are configured to ensure the thick fine        tailings has a turbulent flow regime upon addition of the        flocculant;    -   a floc build-up pipeline assembly in fluid communication with        the in-line addition assembly and configured to shear the        in-line flow of the flocculating tailings material to increase a        yield stress thereof and to produce a non-turbulent in-line flow        of flocculated material;    -   a shear conditioning pipeline assembly configured to shear        condition the non-turbulent in-line flow of flocculated material        to decrease the yield stress thereof and produce a conditioned        flocculated tailings material that is within a water release        zone wherein water separates from the conditioned flocculated        tailings material; and    -   a dewatering unit in fluid communication with the shear        conditioning pipeline assembly for receiving and dewatering the        conditioned flocculated tailings material.

In some implementations, the pump, the feed pipeline assembly and thein-line addition assembly are configured to provide the in-line flow ofthe thick fine tailings with a Bingham Reynolds Number of at least40,000 upon addition of the flocculant.

In some implementations, the pump, the feed pipeline assembly and thein-line addition assembly are configured to provide the in-line flow ofthe thick fine tailings with a Bingham Reynolds Number of at least50,000 upon addition of the flocculant.

In some implementations, the pump, the feed pipeline assembly and thein-line addition assembly are configured to provide the in-line flow ofthe thick fine tailings with a Bingham Reynolds Number of at least60,000 upon addition of the flocculant.

In some implementations, the pump, the feed pipeline assembly and thein-line addition assembly are configured to provide the in-line flow ofthe thick fine tailings with a Bingham Reynolds Number of between 40,000and 65,000 upon addition of the flocculant.

In some implementations, the pump, the feed pipeline assembly and thein-line addition assembly are configured to provide the in-line flow ofthe thick fine tailings with a Bingham Reynolds Number of between 45,000and 60,000 upon addition of the flocculant.

In some implementations, the pump is configured to provide a feed flowrate of the thick fine tailings above a minimum threshold to ensure theturbulent flow regime.

In some implementations, the feed pipeline assembly and the in-lineaddition assembly are configured to have a sufficiently small pipediameter to ensure the turbulent flow regime.

In some implementations, the pump, the floc build-up pipeline assemblyand the shear conditioning pipeline assembly are configured to such thatthe non-turbulent in-line flow of flocculated material has a laminarflow regime.

In some implementations, the pump is configured to operate at asubstantially constant flow rate. In some implementations, the pump isconfigured to operate at substantially constant rotations per minute.

In some implementations, the in-line addition assembly comprising aninjector for adding a solution comprising the flocculant into thein-line flow of the thick fine tailings.

In some implementations, the system also includes a flocculant additioncontroller for controlling the addition of the flocculant into thein-line flow of the thick fine tailings.

In some implementations, the flocculant addition controller isconfigured to provide ratio control of the flocculant with respect tothe in-line flow of the thick fine tailings.

In some implementations, the dewatering unit comprises a sub-aerialdeposition site. In some implementations, the dewatering unit comprisesa thickener and/or a filter.

In some implementations, there is provided a method of treating thickfine tailings, comprising:

-   -   dispersing a flocculant into the thick fine tailings having a        turbulent flow regime to produce a turbulent flocculating        tailings material;    -   subjecting the turbulent flocculating tailings material to shear        to build-up flocs and increase a yield stress thereof, to        produce a flocculated material having a non-turbulent flow        regime; and    -   shear conditioning the flocculated material to decrease the        yield stress thereof and produce a conditioned flocculated        tailings material that is within a water release zone wherein        water separates from the conditioned flocculated tailings        material; and    -   dewatering the conditioned flocculated tailings material.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 40,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 50,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 60,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of between 40,000 and 65,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of between 45,000 and 60,000 upon addition of the flocculant.

In some implementations, the dispersing of the flocculant into the thickfine tailings is performed in-line.

In some implementations, the step of subjecting the turbulentflocculating tailings material to shear is performed in-line.

In some implementations, the step of shear conditioning the flocculatedmaterial is performed in-line.

In some implementations, providing the turbulent flow regime comprisesregulating a feed flow rate of the thick fine tailings above a minimumthreshold.

In some implementations, providing the turbulent flow regime comprisesconfiguring a pipeline assembly that transports the thick fine tailingsfor addition of the flocculant and transports the flocculating tailingsafter addition of the flocculant, to have a sufficiently small pipediameter.

In some implementations, providing the turbulent flow regime comprisesensuring a sufficiently low viscosity of the thick fine tailings uponaddition of the flocculant.

In some implementations, the flocculated material has a laminar flowregime.

In some implementations, the dewatering comprises depositing theconditioned flocculated tailings material onto a sub-aerial depositionsite.

In some implementations, the dewatering comprises subjecting theconditioned flocculated tailings material to thickening and/orfiltering.

In some implementations, there is provided a method of treating thickfine tailings, comprising:

-   -   providing a thick fine tailings flow in an upstream pipeline        section;    -   contacting the thick fine tailings flow with a flocculant to        produce a flocculation tailings in a dispersion pipeline zone;    -   transporting the flocculation tailings through a downstream        pipeline section; and    -   dewatering the flocculation tailings;    -   wherein the upstream pipeline section and the dispersion        pipeline zone are configured and the thick fine tailings flow is        provided so as to have a turbulent flow regime in both the        upstream pipeline section and the dispersion pipeline zone.

In some implementations, the thick fine tailings flow has a flow ratethat is controlled in accordance with rheological characteristics of thethick fine tailings and pipe diameter of the upstream pipeline section.

In some implementations, the upstream pipeline section has a pipediameter of at most 12 inches and the dispersion pipeline zone has apipe diameter sufficient to ensure turbulence and mixing in thedispersion pipeline zone.

In some implementations, the dispersion pipeline zone has a pipediameter of at most 6 inches.

In some implementations, the downstream pipeline section has a pipediameter sufficiently large such that the flocculation tailings flowingtherethrough has a non-turbulent flow regime.

In some implementations, the downstream pipeline section has a pipediameter sufficiently large such that the flocculation tailings flowingtherethrough has a laminar flow regime.

In some implementations, the thick fine tailings comprise mature finetailings (MFT). In some implementations, the thick fine tailingscomprises tailings derived from an oil sands extraction operation. Insome implementations, the thick fine tailings are retrieved from atailings pond.

In some implementations, there is provided a method of treating thickfine tailings, comprising:

-   -   dispersing a flocculant into the thick fine tailings to produce        a flocculating tailings material;    -   subjecting the flocculating tailings material to shear to        build-up flocs and increase a yield stress thereof, to produce a        non-turbulent in-line flow of flocculated material;    -   shear conditioning the non-turbulent in-line flow of flocculated        material to decrease the yield stress thereof and produce a        conditioned flocculated tailings material that is within a water        release zone wherein water separates from the conditioned        flocculated tailings material,    -   managing flow conditions to inhibit backpressure oscillations        caused by increased yield stress of the flocculated tailings;        and    -   dewatering the conditioned flocculated tailings material.

In some implementations, the step of managing flow conditions comprisesconfiguring a shear conditioning pipeline assembly transporting thenon-turbulent in-line flow of flocculated material to have asufficiently large pipe diameter to inhibit backpressure oscillations.

In some implementations, the step of configuring the shear conditioningpipeline assembly is performed based on properties of the non-turbulentin-line flow of flocculated material. In some implementations, theproperties include yield stress.

In some implementations, the step of configuring the shear conditioningpipeline assembly is performed based on flow rates of the thick finetailings and/or the non-turbulent in-line flow of flocculated material.

In some implementations, the step of managing flow conditions comprisesproviding a turbulent flow regime of the thick fine tailings uponcontact with the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 40,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 50,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of at least 60,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of between 40,000 and 65,000 upon addition of the flocculant.

In some implementations, the thick fine tailings has a Bingham ReynoldsNumber of between 45,000 and 60,000 upon addition of the flocculant.

In some implementations, the dispersing of the flocculant into the thickfine tailings is performed in-line. In some implementations, the step ofsubjecting the flocculating tailings material to shear is performedin-line. Alternatively, such steps may be performed in devices otherthan pipelines and such devices may be interconnected by pipes totransfer the fluid.

In some implementations, providing the turbulent flow regime comprisesregulating a feed flow rate of the thick fine tailings above a minimumthreshold.

In some implementations, providing the turbulent flow regime comprisesconfiguring a pipeline assembly that transports the thick fine tailingsfor addition of the flocculant and transports the flocculating tailingsafter addition of the flocculant, to have a sufficiently small pipediameter.

In some implementations, providing the turbulent flow regime comprisesensuring a sufficiently low viscosity of the thick fine tailings uponaddition of the flocculant.

In some implementations, the non-turbulent in-line flow of flocculatedmaterial has a laminar flow regime.

In some implementations, the dewatering comprises depositing theconditioned flocculated tailings material onto a sub-aerial depositionsite.

In some implementations, the dewatering comprises subjecting theconditioned flocculated tailings material to thickening and/orfiltering.

In some implementations, the flocculant is provided as a flocculantsolution. In some implementations, the flocculant solution has aconcentration of flocculant of 0.1 wt. % to 1 wt. %. In someimplementations, the flocculant solution is an aqueous solutioncomprising ≦5 wt. %, ≦2 wt. %, ≦1.5 wt. %, or ≦1 wt % of the flocculant.In some implementations, the flocculant solution is an aqueous solutioncomprising ≦1 wt. %, ≦0.6 wt. % or ≦0.4 wt. % of the flocculating agent.In some implementations, the flocculant comprises an anionic polymerflocculant.

In some implementations, the step of managing flow conditions isprovided so as to attenuate oscillations in thick fine tailings flowrate to an average attenuated oscillation amplitude of at most 20 m³/hr.In some implementations, the step of managing flow conditions isprovided so as to attenuate oscillations in flocculant flow rate to anaverage attenuated oscillation amplitude of at most 5 m³/hr.

In some implementations, the step of managing flow conditions comprises:pumping the thick fine tailings using a first pump; controlling thefirst pump based on a flow rate set point of the thick fine tailings;pumping the flocculant solution using a second pump; controlling thesecond pump based on a flow rate set point of the flocculant solution;and regulating the flow rate set point of the flocculant solution basedon flow rate, density and/or clay content of the thick fine tailings. Insome implementations, the first and second pumps are centrifugal pumps.In some implementations, the first and second pumps are positivedisplacement pumps.

In some implementations, the step of managing flow conditions comprisesavoiding flow restrictions with respect to the non-turbulent in-lineflow of flocculated material. In some implementations, the step ofmanaging flow conditions comprises avoiding obstructions with respect tothe non-turbulent in-line flow of flocculated material. In someimplementations, the step of managing flow conditions comprises avoidingpipeline diameter reductions with respect to the non-turbulent in-lineflow of flocculated material. In some implementations, the step ofmanaging flow conditions comprises providing a substantially constantpipe diameter for transporting the flocculating tailings material andthe non-turbulent in-line flow of flocculated material.

In some implementations, there is provided a method of treating thickfine tailings, comprising:

-   -   pumping the thick fine tailings to provide an in-line thick fine        tailings flow;    -   pumping a flocculant solution comprising a flocculant to provide        an in-line flocculation solution flow,    -   contacting the in-line thick fine tailings flow with the in-line        flocculant solution flow to produce a flocculation tailings;    -   shear conditioning the flocculation tailings to produce a        conditioned flocculated tailings material;    -   dewatering the conditioned flocculated tailings material; and    -   implementing a flow control strategy comprising:        -   setting a substantially constant flow rate for the in-line            thick fine tailings flow;        -   setting a substantially constant flocculant dosage of the            in-line flocculant solution flow based on flow rate, density            and/or clay content of the in-line thick fine tailings flow;            and        -   wherein the substantially constant flow rate of the in-line            thick fine tailings flow is above a minimum threshold to            provide sufficient turbulence to substantially attenuate            oscillations in both the flow rate of the in-line flocculant            solution flow and the in-line thick fine tailings flow.

In some implementations, the flow rate of the thick fine tailings flowis turbulent. In some implementations, the flow rate is at least 400m³/hr within a pipeline having a diameter of at most 12 inches.

In some implementations, the flow management comprises providing a flowrate in the pipeline that is turbulent and related to the size of thepipeline and the characteristics of the thick fine tailings.

In some implementations, the flocculant flow comprises a solution havinga concentration of flocculating agent between 0.1 wt. % to 1 wt. %. Insome implementations, the flocculant is an anionic polymer flocculant.In some implementations, the solution comprising the flocculating agentis an aqueous solution comprising ≦5 wt. %, ≦2 wt. %, ≦1.5 wt. %, or ≦1wt. % of said flocculating agent. In some implementations, the solutioncomprising the flocculating agent is an aqueous solution comprising ≦1wt. %, ≦0.6 wt. % or ≦0.4 wt. % of said flocculating agent.

In some implementations, the flow rate of the in-line thick finetailings flow is sufficient to attenuate oscillations in thick finetailings flow rate to an average attenuated oscillation amplitude of atmost 20 m³/hr. In some implementations, the flow rate of the in-linethick fine tailings flow is sufficient to attenuate oscillations inflocculant flow rate to an average attenuated oscillation amplitude ofat most 5 m³/hr. In some implementations, the flow rate of the in-linethick fine tailings flow is sufficient to attenuate oscillations inthick fine tailings flow rate and/or attenuate oscillations inflocculant flow rate by at least 90% based on average oscillationamplitude.

In some implementations, there is provided a method for attenuatingoscillations in flow rates of an in-line flocculant solution flowcomprising a flocculant and an in-line thick fine tailings flow that arecontacted together, comprising providing the in-line thick fine tailingsflow with a flow rate above a minimum threshold to provide a turbulentflow regime upon contact with the in-line flocculant solution flowsufficient to disperse the flocculant into the thick fine tailings andproduce an in-line flocculation tailings flow having a substantiallystable rheological profile along a downstream pipeline.

In some implementations, the minimum threshold is sufficient such thatthe in-line thick fine tailings flow has a Bingham Reynolds Number of atleast 40,000 upon contact with the flocculant solution.

In some implementations, the minimum threshold is sufficient such thatthe in-line thick fine tailings flow has a Bingham Reynolds Number of atleast 50,000 upon addition of the flocculant solution.

In some implementations, the minimum threshold is sufficient such thatthe in-line thick fine tailings flow has a Bingham Reynolds Number of atleast 60,000 upon addition of the flocculant solution.

In some implementations, the minimum threshold is sufficient such thatthe in-line thick fine tailings flow has a Bingham Reynolds Number ofbetween 40,000 and 65,000 upon addition of the flocculant solution.

In some implementations, the minimum threshold is sufficient such thatthe in-line thick fine tailings flow has a Bingham Reynolds Number ofbetween 45,000 and 60,000 upon addition of the flocculant solution.

In some implementations, addition of the flocculant solution isperformed by ratio control with respect to the in-line flow of the thickfine tailings. In some implementations, the ratio control comprisesvolumetric ratio control or mass ratio control.

In some implementations, there is provided a method for attenuatingoscillations in a flow rate of a flocculant solution comprising aflocculant injected into a flow of thick fine tailings, comprisingreducing and/or inhibiting and/or minimizing air content in theflocculant solution prior to injection.

In some implementations, reducing air content comprises reducing aviscosity of the flocculant solution sufficient to promote airliberation. In some implementations, reducing the viscosity of theflocculant solution comprises reducing a concentration of the flocculanttherein. In some implementations, reducing the concentration of theflocculant comprises reducing by 50%. In some implementations, reducingthe concentration of the flocculant comprises reducing to at most 1 wt %flocculant per total weight of the flocculant solution.

In some implementations, the method also includes providing the flow ofthick fine tailings with a turbulent flow regime. In someimplementations, the flow of thick fine tailings has a Bingham ReynoldsNumber of at least 40,000 upon contact with the flocculant solution. Insome implementations, the flow of thick fine tailings has a BinghamReynolds Number of at least 50,000 upon contact with the flocculantsolution. In some implementations, the flow of thick fine tailings has aBingham Reynolds Number of at least 60,000 upon contact with theflocculant solution. In some implementations, the flow of thick finetailings has a Bingham Reynolds Number of between 40,000 and 65,000 uponcontact with the flocculant solution. In some implementations, the flowof thick fine tailings has a Bingham Reynolds Number of between 45,000and 60,000 upon contact with the flocculant solution.

It should also be noted that various features and implementationsdescribed above may be combined with other features and implementationsdescribed above and/or herein. For example, one or more features relatedto minimizing air content in the flocculant solution may be combinedwith one or more features related to inhibiting oscillation in the flowrates and/or providing turbulent flow regime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents typical settling layers for tailings ponds.

FIG. 2 represents a general view of a Tailings Reduction Operation (TRO)according to Applicant's technology.

FIG. 2a represents a schematic view of the pumping devices, pipeline andbranches (optionally provided with spigots) according to Applicant'stechnology.

FIG. 3 represents a graph of shear yield stress versus time.

FIG. 4 represents the effect of net water release on the drying timesfor treated mature fine tailings (MFT) deposits.

FIG. 5 represents laboratory phases of MFT.

FIGS. 6 and 7 represent variations net water release and flow rate in aTRO.

FIG. 8 represents a flow regime model output for MFT.

FIG. 9 represents average mature fine tailings flow rates and net waterrelease for a MFT.

FIG. 10 represents variations of net water release and strength offlocculated MFT versus the length of a pipeline.

FIG. 11 represents an initial header design.

FIG. 12 represents oscillations of process variables of MFT flow,flocculant solution discharge pressure and flocculant solution flow.

FIG. 13 represents visual depiction of flocculation process as mixingand conditioning occur over time with varying clay to water ratios.

FIG. 14 represents an oscillating flocculant dose when sampled at veryshort intervals.

FIG. 15 represents an example of a modified header.

FIGS. 16 and 17 represent that the modified header configuration withless restrictions and lower backpressure swing susceptibility, leads tosignificantly lower or attenuated flow oscillations of the streams ofthe dewatering system compared to the former header.

FIG. 18 represents notable benefits in the Net Water Release (NWR) usingthe modified header configuration.

FIG. 19 represents when the flow rate of the MFT is below a minimumthreshold, the system can experience significantly higher oscillations.

FIG. 20 represents that below a minimum flow rate, the dispersion of theflocculant into the MFT may not complete sufficiently in the proximatesection of the pipeline, but rather completes further down the pipeline.

FIG. 21 illustrates that at a minimum flow rate threshold, the MFTturbulence facilitates dispersion to occur in the pipeline sectionproximate to the flocculant addition point.

FIGS. 22 and 23 illustrate various flow parameters are shown for the1.5% and 1% flocculant solutions.

DETAILED DESCRIPTION

The present invention relates to the dispersion and/or handling offlocculation tailings in order to enhance the dewatering operation ofthick fine tailings.

Some techniques for enhancing the dewatering process concern reducing orattenuating oscillations in the flow of certain streams. Flowoscillations in the thick fine tailings or flocculant streams can causevariations in the dewatering operations that reduce performance. Beforeelaborating on the various techniques for reducing oscillations andimproving the dewatering operations, some general descriptions will beprovided.

Introduction and General Overview

In some implementations, the thick fine tailings are suspensions derivedfrom an oil sands mining operation and are oil sands mature finetailings (MFT) stored in a tailings pond. For illustrative purposes, thetechniques described below are described in reference to this exampletype of thick fine tailings, i.e., MFT, however, it should be understoodthat the techniques described can be used for thick fine tailingsderived from sources other than an oil sands mining operation.

Referring to FIG. 1, tailings are left over material derived from amining extraction process. By way of illustrative example, the miningextraction process can be a process for extracting bitumen from the oilsands.

“Thick fine tailings” are suspensions derived from a mining operationand mainly include water and fines. The fines are small solidparticulates having various sizes up to about 44 microns. The thick finetailings have a solids content with a fines portion sufficiently highsuch that the fines tend to remain in suspension in the water and thematerial has slow consolidation rates. More particularly, the thick finetailings may have a ratio of coarse particles to the fines that is lessthan or equal to 1. The thick fine tailings has a fines contentsufficiently high such that flocculation of the fines and conditioningof the flocculated material can achieve a two phase material whererelease water can flow through and away from the flocs. For example,thick fine tailings may have a solids content between 10 wt % and 45 wt%, and a fines content of at least 50 wt % on a total solids basis,giving the material a relatively low sand or coarse solids content. Thethick fine tailings may be retrieved from a tailings pond, for example,and may include what is commonly referred to as “mature fine tailings”(MFT).

“MFT” refers to a tailings fluid that typically forms as a layer in atailings pond and contains water and an elevated content of fine solidsthat display relatively slow settling rates. For example, when wholetailings (which include coarse solid material, fine solids, and water)or thin fine tailings (which include a relatively low content of finesolids and a high water content) are supplied to a tailings pond, thetailings separate by gravity into different layers over time. The bottomlayer is predominantly coarse material, such as sand, and the top layeris predominantly water. The middle layer is relatively sand depleted,but still has a fair amount of fine solids suspended in the aqueousphase. This middle layer is often referred to as MFT. MFT can be formedfrom various different types of mine tailings that are derived from theprocessing of different types of mined ore. While the formation of MFTtypically takes a fair amount of time when derived from certain wholetailings supplied form an extraction operation (e.g., between 1 and 3years under gravity settling conditions in the pond), it should be notedthat MFT and MFT-like materials may be formed more rapidly depending onthe composition and post-extraction processing of the tailings, whichmay include thickening or other separation steps that may remove acertain amount of coarse solids and/or water prior to supplying theprocessed tailings to the tailings pond.

It should be understood that the systems and techniques described hereincan be applied to thick fine tailings derived from mining operationsother than oil sands mining operations. For illustrative purposes, someof the techniques and systems are described below in the context ofthick fine tailings derived from oil sands mining operations, includingfor example mature fine tailings (MFT), but it should be understood thatother types of thick fine tailings could also be used.

In the context of oil sands, tailings may include fine and coarsemineral particles, water and residual bitumen. Tailings may be stored inlarge reservoirs called tailings ponds. FIG. 1 displays typical settlinglayers for tailings ponds. The coarse mineral material settles out onthe bottom while free process effluent water separates to the top. Themiddle layers are composed of the fine clay particles suspended inwater. Initially, these suspended fines may be referred to as thin finetailings (TFT) before consolidating typically over the course of two tothree years and becoming mature fine tailings (MFT) which is an exampleof thick fine tailings.

FIG. 2 represents a general view of a dewatering operating for thetreatments of thick fine tailings, such as MFT.

More particularly, as illustrated on FIG. 2a , thick fine tailings 1 maybe pumped by a pump 3 from a tailing pond (as illustrated in FIGS. 1 and2) and flows through a pipeline 5 which is provided with a chemicaladdition portion 7 including an injector 9 for in-line addition of asolution comprising a flocculating agent 11. The pipeline 5 may alsoinclude a downstream portion (which may also be referred to as a“header”) that may include branches 13, optionally provided with outletspigots, allowing deposition of the treated fine tailings 15 onto adeposition area 17.

In some implementations, the pipeline may have certain dimensions toenable improved processing. For example, the feed portion of thepipeline for supplying the thick fine tailings feed flow to theflocculent injection point may be sized, configured and operated suchthat the thick fine tailings feed flow has a turbulent flow regime toensure dispersion of flocculant into the thick fine tailings; the flocbuild-up portion of the pipeline downstream of the flocculent injectionpoint may be sized, configured and operated such that the flocculatingtailings material transition from turbulent to laminar flow as thematerial undergoes floc build-up and increases in yield stress; and theconditioning portion of the pipeline downstream of the floc build-upportion may be sized, configured and operated such that the flocculatedmaterial has a laminar flow regime and undergoes floc breakdown untilreaching water release zone and is thus deposited. Each of the pipelineportions may be sized, configured and operated according to certainmethods and/or constraints that may be present, as will be explainedfurther below. For example, the feed portion of the pipeline may beprovided based on ensuring turbulence of the thick fine tailings feed,the floc build-up portion of the pipeline may be provided based oncomputational fluid dynamic (CFD) modelling to reach a peak yield stresslevel to complete floc build-up, and the floc breakdown portion of thepipeline may be provided based on a pre-determined shear parameter, suchas the Camp Number, that may be derived in a laboratory setting.

In some implementations, the entire pipeline has substantially the samediameter and thus the operation may be adapted and controlled byproviding certain flow rates, fluid properties, pipe lengths, and so on,to achieve the desired effects in each pipeline portion for effectiveflocculation and dewatering. Alternatively, the pipeline portions mayhave different diameters, and the operation may be adapted accordingly.In some implementations, the floc build-up and floc breakdown portionsof the pipeline may have a 12 inch diameter, and may also have anoverall length from the chemical addition portion 7 to the outletspigots of less than 100 meters. It should be understood that variousother diameters and lengths of pipeline may be used in conjunction withthe operating conditions that are implemented. In addition, varioustypes of pumps may be used to move the fluid through the pipeline, anddepending on the type and horsepower of the pumps the pipeline andoperating conditions may be adjusted. More regarding the above will bediscussed further below.

FIG. 3 illustrates general stages of the flocculation reaction overtime, particularly in relation to static yield stress.

FIG. 4 displays the effect of Net Water Release (NWR) has on the dryingtimes of flocculated fine tailings. NWR is a metric that has beendeveloped and is a measure of the differential in water between thestarting thick fine tailings and the treated and drained thick finetailings after a given draining time. In other words, NWR is adifference in moisture contents. The draining time may be 24 hours, 12hours, 20 minutes, or 19 minutes, for example, or another representativetime period for drainage in commercial applications. There are two mainways to calculate the NWR by volumetric or solid content difference.Example formula to calculate the NWR are as follows:

${NWR} = ( \frac{\begin{matrix}{{{Quantity}\mspace{14mu} {of}\mspace{14mu} {water}\mspace{14mu} {Recovered}} -} \\{{Quantity}\mspace{14mu} {of}\mspace{14mu} {Flocculant}\mspace{14mu} {Water}\mspace{14mu} {Added}}\end{matrix}}{{Quantity}\mspace{14mu} {of}\mspace{14mu} {initial}\mspace{14mu} {Final}\mspace{14mu} {Tailings}\mspace{14mu} {Water}} )$${NWR} = {1 - ( \frac{1}{{{tMFT}\mspace{14mu} {wt}\mspace{14mu} \% \mspace{14mu} {mineral}} + {{wt}\mspace{14mu} \% \mspace{14mu} {Bitumen}} - 1} ) + ( \frac{1}{{{MFT}\mspace{14mu} {wt}\mspace{14mu} \% \mspace{14mu} {mineral}} + {{wt}\mspace{14mu} \% \mspace{14mu} {Bitumen}} - 1} )}$

A NWR test may be conducted using immediate drainage of a flocculationtailings sample for a drainage time of about 20 minutes. In this regard,for optimal dosage range and good flocculation, the water release in 10or 20 minutes may be about 80% of the water release that would occurover a 12 to 24 hour period. For underdosed or overdosed samples, thewater release in 20 minutes may be about 20% to 60% of the water releasethat would occur over a 12 to 24 hour period. The 20 minute NWR test maytherefore be followed by a longer NWR test, e.g. 12 hour drainage time,which may use a water volume or solids content measurement approach. Itis also noted that the laboratory and field tests described herein useda volumetric 24 hour NWR test. Referring back to FIG. 4, it can be seenthat a greater initial water release results in a shorter dryingduration that is required to achieve a certain solids target. The NWR isdependent on several factors, including the dispersion of the flocculantinto the thick fine tailings and the subsequent conditioning (includingmixing) of the flocculation tailings. Rapid and thorough dispersion ispreferred for increasing NWR.

FIG. 5 displays four regions of flocculated tailings (also identified astMFT) behaviour that have been observed. FIG. 5 is similar to FIG. 3,but its stages will be presented in a slightly different manner.

As can be seen from FIG. 5, the rheological evolution of thick finetailings, such as MFT, that is subjected to flocculation may include thefollowing stages:

-   -   (a) A dispersion stage where a flocculation reagent is rapidly        mixed into the fine tailings and the flocculation begins,        forming the flocculation tailings material.    -   (b) A floc build-up stage where the flocculation tailings        material increases in yield stress. In this stage, the        flocculation tailings material reaches a peak yield stress. Up        to and around this peak yield stress the flocculation tailings        material may be said to be “under-mixed” because insufficient        mixing or conditioning has been performed to begin to breakdown        the flocculated matrix and allow increased water release. FIG. 5        shows that the water release is effectively nil up to a certain        point just after the peak yield stress, after which the water        release increases up to an initial maximum. Within this floc        build-up and under-mixed stage, the flocculation tailings        material can resemble a gel state material and this stage also        becomes smaller with improved dispersion.    -   (c) A floc breakdown stage where the flocculation tailings        material decreases in yield shear stress. This stage includes a        water release zone where water is released from the flocculated        matrix. FIG. 5, for example, illustrates the water release zone        beginning at a certain point within the floc breakdown stage,        after the peak water release, and spanning a certain mixing time        interval over which the water release gradually decreases. In        this stage, the flocculated matrix takes on a more permeable        state and water is released at within the water release zone.    -   (d) An over-shear zone, which is avoided, where the flocs are        broken down to a point that the material generally returns to a        similar states as the initial fine tailings. Little to no water        can release from the broken down flocculation matrix.

In order to facilitate efficient dewatering operations, it is desirablethat the flocculation tailings material be deposited within the waterrelease zone in a consistent manner.

Inhibiting Process Oscillations

In the flocculation and dewatering operation, the properties of thefluids are relatively complex and undergo rheological evolutionthroughout the process. Oscillations in flow rates, pressures, andflocculated material quality were observed for certain configurations ofthe pipeline. The oscillations were found to be a symptom of certainconfigurations and operating parameters of the overall system.

In one example configuration, the pumps supplying the MFT feed were nearmaximum capacity and the feed flow rate was laminar, transitional orborderline turbulent entering the flocculent injection point. The amountof flocculant addition required to achieve optimally dosed MFT isaffected by the initial dispersion of flocculant into the MFT. Inparticular, poor dispersion has higher dosing requirements to achieve anoptimally dosed MFT. The efficacy of dispersion can be affected by anumber of parameters including MFT flow regime with good dispersionoccurring when MFT is in turbulent flow. In addition, the flocculationtailings material has different rheology depending on whether the thickfine tailings are optimally dosed, overdosed or underdosed withflocculant. When optimally dosed, the flocculated material attains thehighest yield stress causing highest backpressure in the pipeline. Whenunderdosed or overdosed, the flocculated material attains a lower yieldstress causing lower backpressures in the pipeline. Thus, as theflocculant dosage approaches optimal, the backpressure in the pipelineincreases to a maximum. In turn, the pumps transporting the fluid wereoperating at fixed RPM (not flow controlled), since the pumps were atmaximum capacity. With fixed pump RPM, as backpressure increases due tooptimal flocculant dosing, the line pressure increases and therefore thethick fine tailings flow rate decreases for the fixed RPM operation ofthe pumps. Furthermore, the flocculant addition was performed by addinga flocculant solution which was ratio controlled according to the flowrate of the thick fine tailings to target a constant dose setpoint. Thedecrease in the flow rate of the thick fine tailings can lead to adecrease in flocculant dosing with a minor lag time. Moreover, withreduced MFT flowrates, reduced dispersion of flocculant occurred. Asmentioned above, poor dispersion results in inefficient flocculate useand in a higher flocculant dose requirement to achieve optimally dosedconditions. With flocculant dose kept constant using a control system,the MFT became underdosed or non-optimally dosed. As mentioned above,non-optimal flocculant dosing, such as underdose, leads to a reductionin the yield stress of the flocculated tailings material which, in turn,causes the backpressure in the line to decrease. Again, since the pumpshave a fixed RPM, the flow rate of the thick fine tailings increases inresponse to the decrease in line backpressure, returning to turbulentflow regime with good dispersion and optimal flocculant dosingconditions per the constant dose setpoint maintained by the controlsystem. This leads again to the higher backpressure issues. In thismanner, the process experienced cyclical or oscillatory operations.

The dewatering system may be configured and operated to inhibit processoscillations. Inhibiting oscillations may be performed using variousmethods depending on the dewatering system equipment and constraints.For example, an existing system including certain components may beretrofitted and/or operated to as to inhibit oscillations; or a systemmay be designed, constructed and operated so as to inhibit oscillations.In some implementations, the thick fine tailings flow is provided with aturbulent flow regime upon addition of the flocculant. Flocculantinjectors enabling turbulence eddies have been implemented in thecontext of flocculating and dewatering thick fine tailings. However, itis also advantageous to provide the flow of the thick fine tailingsitself in a turbulent flow regime upon addition of the flocculant.Providing turbulent pipe flow may include pumping the thick finetailings above a minimum flow rate threshold for a given pipe diameter,configuring the pipeline so as to have sufficient dimensions (e.g., pipediameter), pre-treating the thick fine tailings so as to reduce theviscosity thereof, or other methods of providing a high Reynolds Number.

In some scenarios, where existing pumps and piping provide certainconstraints such as pumps being at maximum capacity, oscillations inbackpressure may also be reduced by modifying the portions of thepipeline that receive and transport the higher yield stress material. Inone example, it was found that changing the header pipe diameter (e.g.,from 8″ diameter piping to 12″ piping) reduced oscillations and improvedconsistent flocculation and deposition in the water release zone. Thesechanges also contributed to allowing for higher flow rates that remainedsteadier as well as a more stable discharge pressure. More regardingsuch scenarios will be discussed further below in relation to theimplementation of a modified header design in an existing dewateringoperation.

In some scenarios, the dewatering system is configured to include pipinghaving sufficient strength for high pressures and pumps that can providesufficient force to provide thick fine tailings feed flow rates to beabove the turbulent transition point regardless of the downstream pipingconfiguration. In order to ensure turbulent conditions, the feed of thethick fine tailings is provided with a turbulent flow regime for optimalflocculant dosing (i.e., the flocculant dosing which results in thehighest yield stress and backpressure scenario).

Various implementations, observations and data will now be discussed inrelation to certain ways of inhibiting process oscillations in a thickfine tailings dewatering operation.

FIGS. 6 and 7 show process data for a dewatering operation which wasmodified by removing an in-line mixer that was usually present justdownstream of flocculant addition. The mixer was a set of bafflesprovided across the pipeline after the injector and defining a secondstage mixer. These figures represent data gathered from laboratoryresults and process data for four cells tested over an operating seasonbefore and after the mixers were removed. They also show that there wasa general increase in the NWR trend along with an increase in the flowrates at these cells after the mixers were removed. Removing the mixercan be viewed as reducing a restriction on the downstream pipelineconfiguration to flocculation tailings flow.

Table 1 shows MFT flow rates, flocculating agent dosage and NWR fordeposition cells affected by the mixer removal trial, while Table 2 hasdata from other deposition cells for comparison purposes. In thesetables, the term “polymer” corresponds to the flocculating agent whichwas a polymer flocculant (in particular a 30% charge anionicpolyacrylamide-sodium polyacrylate co-polymer with a molecular weightover 10,000,000). The table for the first deposition cells demonstratesan increase in the mature fine tailings flow rate and a decrease in theflocculating agent dosage. For the other cells, which operated withmixers, it can be seen that there is an increase in the flow rate whilethe flocculating agent dosage remained relatively constant. The removalof the mixer appears to have aided in the flocculant dispersion for thefirst deposition cells with the mixers removed, as the flocculant dosageand polymer solution flow rates to acquire higher NWR are lower. It canalso be seen that in the other cells the NWR increases significantly aswell with the increase in MFT flow rate.

TABLE 1 South Cells 1, 2, 3 and 4 Before and After Komax Mixer RemovalDosage MFT Flow Polymer Sol. Polymer NWR on clay Status (m³/hr) Flow(m³/hr) Dosage (ppm) (%) basis (ppm) Before 319 55.4 1803 9% 2391 After398 43.8 1303 18% 1544

TABLE 2 North Cells 1, 2, 3 and 4 Before and After Komax Mixer RemovalDosage MFT Flow Polymer Sol. Polymer NWR on clay Status (m³/hr) Flow(m³/hr) Dosage (ppm) (%) basis (ppm) Before 337 41.2 1271 16% 1706 After367 41.7 1181 26% 1619

Table 3 shows an overview of a thick fine tailings flow regime analysismodel. Using the inputs of inner pipe diameter, pipe roughness, MFTdensity and MFT flow rate, the flow regime model analyzes the wallstresses that should be overcome for the flow of MFT to becometurbulent. The main outputs from this model include the flow regime, thetheoretical effective viscosity, the Bingham Reynolds Number and theactual wall stress.

TABLE 3 MFT Bingham Flow Regime Model Plastic Pipe Information Pipe NPS12 in 0.30 m Pipe ID 9.746 in 0.2475 m Pipe Area 74.601  in2 0.05  m2Pipe Roughness 0.0015 mm 1.5E−06 m Fluid Information MFT Density 1.40 SG1400 kg/m3 % Solids 45.89% Yield Stress, T_(y) 5.945 Pa PlasticViscosity, μ_(p) 12.9016 mPas 0.01290 Pas Flow Information MFT Flowrate(m3/hr) 250 275 300 325 350 375 400 425 450 475 500 Bulk Flow Velocity(m/s) 1.44 1.59 1.73 1.88 2.02 2.16 2.31 2.45 2.60 2.74 2.89 InitialLaminar Wall Stress, T_(wi) (Pa) 8.53 8.59 8.65 8.71 8.77 8.83 8.89 8.959.01 9.07 9.13 Bingham Laminar Regime Actual Laminar Wall Stress, T_(wl)(Pa) 7.57 7.66 7.76 7.85 7.94 8.02 8.11 8.19 8.27 8.36 8.44 LaminarStress Ratio (ξ_(l)) 0.79 0.78 0.77 0.76 0.75 0.74 0.73 0.73 0.72 0.710.70 Laminar Bulk Velocity, V_(lam) (m/s) 1.44 1.59 1.73 1.88 2.02 2.162.31 2.45 2.60 2.74 2.89 Laminar To Bulk Flow Error (m/s) 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bingham Turbulent Regime ActualTurbulent Wall Stress, T_(wt) (Pa) 6.86 7.53 8.70 10.37 12.33 14.4316.62 18.90 21.26 23.70 26.23 Turbulent Stress Ratio (ξ_(t)) 0.87 0.790.68 0.57 0.48 0.41 0.36 0.31 0.28 0.25 0.23 Effective Viscosity,μ_(eff) (Pas) 0.0970 0.0612 0.0407 0.0302 0.0249 0.0219 0.0201 0.01880.0179 0.0172 0.0167 Initial Newtonian Velocity, V_(Ni) (m/s) 0.96 1.101.28 1.48 1.68 1.87 2.05 2.23 2.40 2.56 2.72 Bingham Reynolds Number(Re) 3429 6238 10901 17011 23415 29588 35446 41022 46369 51529 56538Churchill Friction Factor, f_(N) 0.01063 0.00887 0.00757 0.00673 0.006210.00587 0.00563 0.00544 0.00529 0.00517 0.00506 Calc. NewtonianVelocity, V_(N) (m/s) 0.96 1.10 1.28 1.48 1.68 1.87 2.05 2.23 2.40 2.562.72 Calc. Newtonian Velocity To Initial Error 0.000 0.000 0.000 0.0000.000 0.000 0.000 0.000 0.000 0.000 0.000 Friction Velocity, V_(f) (m/s)0.0735 0.0740 0.0744 0.0749 0.0753 0.0757 0.0761 0.0765 0.0769 0.07730.0776 Turbulent Bulk Velocity, V_(turb) (m/s) 1.44 1.59 1.73 1.88 2.022.16 2.31 2.45 2.60 2.74 2.88 Turbulent To Bulk Flow Error (m/s) 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Flow Regime AnalysisFlow Regime Laminar Laminar Turbulent Turbulent Turbulent TurbulentTurbulent Turbulent Turbulent Turbulent Turbulent Actual EffectiveViscosity, μ_(eff) (Pas) 0.0602 0.0575 0.0407 0.0302 0.0249 0.02190.0201 0.0188 0.0179 0.0172 0.0167 Actual Bingham Reynolds Number (Re)8311 9560 10901 17011 23415 29588 35446 41022 46369 51529 56538 ActualWall Stress (Pa) 7.57 7.66 8.70 10.37 12.33 14.43 16.62 18.90 21.2623.70 26.23 Note: To run iteration macro. use CTRL + SHIFT + R Lavendercells are the cells set to zero in the Goal Seek iterations Yellow cellsare the cells varied in the Goal Seek iterations

The typical output from the MFT flow regime model can be seen in FIG. 8.This figure is generated by plotting the Bingham Reynolds Number versusthe MFT flow rate. The output seen is dependent on the MFT rheology. Therheological properties of MFT can fluctuate during operation. It can beseen below that for the specific case of 1.42 SG MFT, there is asensitive region around 300-400 m³/hr where the flow regime is in thelaminar to turbulent transition zone.

As mentioned previously, fluctuations in MFT rheology can result inoperating within the laminar or transitional flow regime. Operating inthe laminar or transitional flow regime may significantly affect how theflocculating agent is initially introduced into the MFT. While the flowtravelling through a 6 inch flocculant solution injector may beturbulent at all flow cases, the MFT and the flocculating agent mayimmediately exit the injector back into a 12″ pipe which may be composedof High Density Polyethylene (HDPE). Upon expanding into this size ofpipe, the flow regime at this time may in fact return to the laminar ortransitional zone and inhibit the early stages of flocculating agentdispersion. This can have negative effects on how much water will bereleased during the flocculation and dewatering process.

FIG. 8 also shows that there is preferably a minimum MFT flow ratearound 400 m³/hr that is able to achieve effective flocculating agentdispersion for this pipeline and injector configuration.

As seen from FIG. 9, the MFT flow regime model suggests that there is asensitive region near 300-400 m³/hr for this pipeline and injectorconfiguration. FIG. 9 shows field data from certain dewateringoperations during the course of an operating season. FIG. 9 shows acorrelation between the MFT flow rate and the NWR. At lower flow ratesthe NWR was more sporadic and tended to be worse than at greater flows.As the MFT flow rates decrease, so does the NWR results from thoseoperations. It can be seen that the newer water release resultsfluctuate in between the 300-350 m³/hr zone. This directly supports theresults from the MFT flow regime model and the minimum flowobservations.

Also, as seen from FIG. 10, the length of the pipeline between theinjector 9 and the outlets may affect the NWR. More particularly, itappears that in some implementations, a pipe length of less than 100meters is advantageous to obtain a reliable NWR upon deposition for thispipeline and injector configuration.

Turbulent Flow Regime Operation

As mentioned further above, a turbulent flow regime may be provided toinhibit process oscillations. In some implementations, a turbulent flowregime is provided for the thick fine tailings feed entering theflocculant addition point as well as for the flocculating tailingsmaterial in a section of the floc build-up pipeline. The turbulentsection of the floc build-up pipeline may have a smaller diametercompared to the downstream pipeline and/or the flow rate of the materialmay be provided so as to achieve the turbulence when the section has thesame diameter as the downstream pipeline. In some implementations, theturbulent section of the pipeline has a sufficient length so as toensure dispersion and initial floc build-up. It should be noted thatpipeline may also be coiffured such that when flocculated materialreaches a peak yield stress it transitions to a laminar flow regime andis thereafter transported within the pipeline in a laminar flow regimeto the dewatering unit (e.g., deposition site).

In some implementations, a turbulent flow regime is provided such thatthe thick fine tailings feed has a Bingham Reynolds Number of at least40,000. The Bingham Reynolds Number may be at least 45,000, at least50,000, at least 55,000 or at least 60,000. The Bingham Reynolds Numbermay be provided between 40,000 and 65,000; between 45,000 and 60,000; orbetween 50,000 and 55,000, for example. It should be noted thatoperation within other Bingham Reynolds Number ranges or other ReynoldsNumber ranges that ensure a turbulent flow regime in the dispersionstage and the beginning of the floc build-up stage may be performeddepending on the particularities of the system.

In some implementations, the turbulent flow regime is provided such thatthe thick fine tailings feed has sufficiently high turbulence to enablegood dispersion of the flocculant, and below a maximum threshold thatwould induce the high yield stress flocculated tailings material to alsohave a turbulent flow regime. For example, the flow rate of the thickfine tailings feed may ensure turbulence in the feed and the dispersionstage, while ensuring that the flocculated tailings material is notturbulent or has a laminar flow regime below the laminar-turbulenttransition zone for the high yield stress flocculated material.Providing a laminar flow regime for the flocculated material canfacilitate process control, particularly the shear conditioning stage toachieve the water release zone upon deposition of the conditionedflocculated tailings material. The turbulent flow regime of the feedthick fine tailings may be enabled by controlling the feed flow rate,the feed pipe diameter and/or the feed fluid properties, while thelaminar or non-turbulent flow regime of the flocculated material may beenabled by controlling the feed flow rate and/or configuring thedownstream pipe to have a sufficiently large diameter, for example.

Implementations for Reducing Oscillations in Backpressure and FlocculantDosage

As mentioned above, it had been observed that the commercial scale up ofa pilot MFT dewatering system was experiencing issues related to someoscillations in the quality of the treated MFT that was deposited intothe deposition cells.

It was determined that the design and operation of the conditioningpipeline (also referred to herein as the “header”) transporting theflocculating MFT from the flocculant addition to the deposition cell wasone of the factors leading to oscillations in the quality of thedeposited material. As will be explained below, by modifying the headerof the system the oscillations were reduced without requiring extensivemodifications to operations or other process equipment.

FIG. 11 represents an initial header design. The oscillations in productquality were observed especially when approaching optimal polymer dose.The oscillation issue appeared to affect many of the dewatering systems.During the oscillations, the deposited material could be observed tochange through various levels of quality. Along with the qualityfluctuations, a similar oscillatory behaviour was observed on processvariables such as flows and pressures. For instance, FIG. 12 showsoscillations of process variables of MFT flow, flocculant solutiondischarge pressure and flocculant solution flow.

A number of possible causes of the quality oscillations wereinvestigated. Quality of the deposited flocculated material has asignificant impact on the overall drying paradigm in that material thatreleases water quickly upon deposition results in overall accelerationof the dewatering and drying operation.

It was found that the configuration of the deposition headers incombination with the other equipment and operating parameters for thedewatering process described further above (e.g., pumps at maximumcapacity and not flow rate controlled, flocculant on ratio control, andso on) was leading to backpressure oscillations and other oscillationsin the process.

“Backpressure” may refer to the resistance to the movement of a fluid.Backpressure may be caused by obstructions, restrictions, pipeline bendsor transitions. The term “backpressure” should be generally understoodas resistance to flow. In the context of substantially incompressiblefluids flowing through rigid pipes, as in the present case, a reductionin flow rate at a constricted point means that the flow is “backed up”all the way to the start of the pipe.

As will be understood, in the present case the piping configuration istypically not changing in the sense that there is a header assembly thatis constructed for a given dewatering facility to transfer and conditionthe flocculating tailings from a flocculant addition point to adeposition cell. However, the rheological properties of the flocculatingfluid inside the header assembly are changing which, in turn, changesthe amount of flow resistance generated by the fluid's interaction withobstructions, restrictions, bends and the like.

Hence, to maintain a substantially constant flow, the pressure must beincreased or decreased to account for the changes in flow resistancedepending on the changing rheology. The change in rheology occurs as aresult of the flocculation process when the flocculant is added to theMFT. As the flocs begin the form and build up, the static yield stressof the fluid increases, e.g., up to a maximum value at which pointcontinued shear conditioning begins to thin the fluid, lowering thestatic yield stress. FIG. 13 provides visual depiction of flocculationprocess as mixing and conditioning occur over time with varying clay towater ratios.

FIG. 14 shows the oscillating flocculant dose when sampled at very shortintervals. It can be seen that there are flocculant dosage spikes abovethe optimal dose. This overdosing is due to oscillatory spikes in theMFT flow rate which, in turn, are due to back pressure spikes asexplained further above.

A modified header was provided in order to reduce the backpressure ofthe given dewatering system. The header configuration was modified ontwo of the deposition cells. The modified header included increased pipesize (50% increase in pipe diameter from 8 inches to 12 inches). Anothermodified header may include two splits and have a 12 inch diameter. Themodified header configurations reduced the backpressure of the highyield stress treated MFT (tMFT) at optimal dose, and provided improvedoperations in terms of helping to inhibit oscillations.

FIG. 15 shows an example of the modified header. Upon switching to themodified header configuration, an immediate noticeable difference wasobserved in overall dewatering performance and process stability. Theimpact on process control and stability may be appreciated from acomparison of the process trends illustrated in FIGS. 16 and 17. InFIGS. 16 and 17, the three lines are respectively referring to the MFTflow, the flocculant flow, and the flocculant solution pressure(PIT850).

FIGS. 16 and 17 show that the modified header configuration with lessrestrictions and lower backpressure, lead to significantly lower orattenuated flow oscillations of the streams of the dewatering systemcompared to the former header. FIGS. 16 and 17 not only show that theMFT flow is significantly more stable with the new header configuration,but also that the discharge pressure of the flocculant solutionpreparation unit was lower and more stable.

In addition, referring to FIG. 18, there were notable benefits in theNet Water Release (NWR) using the modified header configuration. The NWRresults with the modified header setup were consistently in the range of30-40% for the entire period of testing with a much lower standarddeviation than results using the previous design.

In some implementations, the conditioning pipeline assembly thattransports the treated MFT to the deposition cells may be configured andoperated for inhibiting fluid oscillations, thereby stabilising thesystem and obtaining more consistent quality material for dewatering.The conditioning pipeline assembly may be configured, for example, byremoving or reducing pipe restrictions, pipe divisions, obstructions,and the like.

In some implementations, a conditioning pipeline assembly may beconfigured and operated in connection with a centrifugal pump that isproviding the hydraulic energy for MFT flow and/or flocculant solutionflow. It may be advantageous to implement a pipeline design with headeras describe above to reduce backpressure oscillations when using acentrifugal pump to displace the MFT, since the MFT flow would not beflow rate controlled.

In some other implementations, a positive displacement pump may be usedfor providing the hydraulic energy for MFT flow and/or flocculantsolution flow. The positive displacement pump can deliver constant flowregardless of changes in downstream pressure and resistance to flow.Utilization of positive displacement pumps may therefore enable improvedstabilization for various different configurations of the conditioningpipeline assembly.

A marked reduction in flocculant dose (in the region of 10-20%) was alsoobserved along with a reduced demand on the flocculant preparation unitdue to lower pressure required for injection. Thus, in addition to thepotential for increased dewatering rate and dried material production,there may also be reduced flocculant dose on average per unit of MFT.While the flocculant reduction amount may vary depending on theproperties of the MFT and operating conditions, and the reduction indose may be relatively small on a per unit basis, the accumulation ofthis flocculant reduction over the course of a full dewatering seasonmay prove to be a significant savings in flocculant cost.

Achieving stable and consistent quality flocculated material can lead tosignificant improvements in the overall dewatering and drying times anddried material production rates. In some scenarios, reduction of fluidrelated oscillations, examples of which are described herein, mayprovide up to two to four times improvement on dried material productionrates.

Furthermore, operation of the dewatering system with increased stabilitymay provide a number of advantages, such as allowing effective and morereliable automation of the system conditions, leading to less operatorinvolvement and reduced equipment alarms or adjustments. In addition,the demand and wear on equipment may also be also reduced, e.g. theflocculant solution preparation unit has lower pressure demands on itsince pressure required for injection of the flocculant solution islower, requiring less flow. This can also allow for operation at higherrates as there may be more room to operate below upper limits.

Providing MFT Flow Rate Above Minimum Threshold

It was also found that for a given dewatering system (which may includeMFT properties such as density and clay-to-water ratio (CWR),conditioning pipeline assembly or header configuration including pipesize and length, polymer flocculant, and so on) there appears to be aminimum MFT flow rate for providing sufficient line pressure andturbulent dispersion of the flocculant into the MFT, for stableoperation within an optimum flocculant dose range.

Referring to FIG. 19, when the flow rate of the MFT is below a minimumthreshold, the system can experience significantly higher oscillations,particularly with regard to the MFT flow rate and the flocculantsolution pressure. PIT850 represents the flocculant solution pressure inkPa. If operating below the minimum flow rate and/or line pressure, theoscillations may still occur and may be quite pronounced in some cases.However, with only a slight increase in flow rate above the minimumthreshold, as can be seen in between time intervals 4 and 5 on FIG. 19,the stability can be dramatically increased as the flow rate andpressure oscillations are attenuated. On FIG. 19, the left Y axis refersto the flow rate of MFT and pressure of the flocculating agent (i.e.,polymer flocculant), and the right Y axis refers to the flowrateflocculating agent (i.e., polymer) flow rate. It should be noted thatthe process may be controlled or the pipeline may be designed such thatthe reduction in process oscillations are similar or at least as greatas the reductions illustrated in FIG. 19.

In some scenarios, if the MFT flow rate is below the minimum threshold,inadequate dispersion of the flocculant into the MFT in the line sectionproximate the flocculant addition point can cause downstream upsets.Referring to FIG. 20, below the minimum flow rate, the dispersion of theflocculant into the MFT may not complete sufficiently in the proximatesection of the pipeline, but rather completes further down the pipelineat locations where there may be bends, restrictions, pipe splits, and soon. In this situation, there are various drawbacks, which may includedeposition of gel like material with little dewatering capacity due toinadequate conditioning to reach the water release stage, variation inthe flocculation material that is deposited out of each spigot due toinadequate dispersion at upstream splits, and/or flow fluctuations.

By operating above the minimum flow rate threshold, the MFT turbulencefacilitates dispersion to occur in the pipeline section proximate to theflocculant addition point, as illustrated in FIG. 21. In such ascenario, the flocculant can be well dispersed into the MFT in the maintransportation section of the pipeline, rather than in any downstreambranches, restriction, spigots or the like. The dispersion stage of theprocess thus has enough time in the upstream section of the pipeline tocomplete and enter the water release stage prior to downstream branches,restrictions, spigots or the like. In addition, flow fluctuations may bereduced or eliminated.

In some implementations, the MFT may thus be provided with a flow rateabove a minimum threshold, sufficient to provide turbulence to promoteproper and stable flocculant dispersion into the MFT.

The configuration and operation of the conditioning pipeline assemblymay also occur in conjunction with ascertaining and providing theminimum threshold of the MFT flow rate, in order to further promoteattenuation of oscillations to achieve increased stability andperformance of the dewatering operation.

Air Removal from Flocculant Solution

It was also observed that air in the flocculant solution can negativelyimpact the dewatering operations.

Air in a pressurized operating pipeline may originate from certainsources. First, prior to start-up, the line may be empty (full of air)and to entirely fill a pipeline with fluid, it is necessary to displacethis air. As the line fills, much of this air will be pushed downstream,but an amount will become trapped at pipeline or system high points. Inaddition, air can be entrained during contacting of dry polymerflocculant with water during polymer flocculant makedown. Dry polymerflocculant is delivered from a hopper to an atmospheric contactingchamber where water is added to the polymer flocculant in what may becalled a Polymer Sluicing unit (PSU). The PSU rotates to improvewater/polymer contact and can form a funnel like flow from the PSU intothe process piping. Also, because the polymer flocculant solution may beviscous, agitation of polymer flocculant and water in the PSU canentrain air. Liquid polymer flocculant solution is routed to a mix tankwere entrained air is slow to exit the solution due to the highviscosity. The polymer flocculant solution leaving the mixing tank isfurther diluted to a final concentration for transport and injectioninto the MFT. Remaining entrained air in the polymer flocculant solutionthat was not released in the mixing tank, will further release fromsolution during the dilution step (which further lowers the viscosity ofthe polymer flocculant) and during transport and agitation in thepipeline. This can continuously add air pockets to the piping system. Apressurized pipeline is typically never without air and sometimes thevolume can be substantial.

It was found that the issue of air in the flocculant solution maycontribute to oscillations in the flocculated tailings quality amongother drawbacks.

Two actions were taken to assess air removal from the flocculantsolution and the pipeline. The first was to install multiple vent pointson the line to release as much air as possible during operation and thecharging of the line. Secondly, the polymer mother solutionconcentration was to be lowered to 1% in order to reduce its viscosityand encourage more air to be released in the preparation unit, e.g. inthe mix tanks prior to final dilution.

A change in flocculant mother solution concentration was made to removemore of the air entrained in the polymer. The change in concentrationfrom 1.5% to 1% by weight reduces the viscosity of the polymer solutionallowing air to be liberated more readily in the upstream mixing tanks.The pipeline was also vented during line charging and at random timesduring the day to release any built up air pockets.

It was found that the flocculant solution flow at the injector showed amarked improvement, for example in terms of the stability of the polymersolution flow through the injector. A more stable flow across theinjector was recorded via a portable flow meter.

Referring to FIGS. 22 and 23, various flow parameters are shown for the1.5% and 1% flocculant solutions. The 1% final flocculant solution hasflow oscillations that are attenuated compared those of the 1.5%solution, thus providing increased injection flow stability.

It is understood that above implementations, aspects and embodiments arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the present invention.

1-135. (canceled)
 136. A method for attenuating oscillations in a flowrate of a flocculant solution comprising a flocculant injected into aflow of thick fine tailings, comprising reducing air content in theflocculant solution prior to injection.
 137. The method of claim 136,wherein reducing air content comprises reducing a viscosity of theflocculant solution sufficient to promote air liberation.
 138. Themethod of claim 137, wherein reducing the viscosity of the flocculantsolution comprises reducing a concentration of the flocculant therein.139. The method of claim 138, wherein reducing the concentration of theflocculant comprises reducing by 50%.
 140. The method of claim 138,wherein reducing the concentration of the flocculant comprises reducingto between 0.1 wt % and 1 wt % flocculant per total weight of theflocculant solution.
 141. The method of claim 137, wherein reducing theviscosity is performed prior to mixing the flocculant solution in orderto promote air liberation during the mixing.
 142. The method of claim141, wherein the mixing is performed in a mixing tank.
 143. The methodof claim 136, wherein the step of removing air from the flocculantsolution comprises venting the flocculant solution.
 144. The method ofclaim 143, wherein the venting is performed at a high point along apressurized pipeline through which the flocculant solution is suppliedfor addition into the thick fine tailings.
 145. The method of claim 144,wherein the venting is performed at multiple high points along thepressurized pipeline.
 146. The method of claim 143, wherein the ventingis performed during line charging and is performed at different times torelease built up air pockets.
 147. The method of claim 136, furthercomprising providing the flow of thick fine tailings with a turbulentflow regime.
 148. A method for treating thick fine tailings, comprising:preparing a flocculant solution comprising a flocculant, water andentrained air; removing air from the flocculant solution to produce anair-depleted flocculant solution; adding the air-depleted flocculantsolution into the thick fine tailings to produce a flocculating tailingsmaterial; shearing the flocculating tailings material to produce aconditioned flocculated tailings material that is within a water releasezone wherein water separates from the conditioned flocculated tailingsmaterial; and dewatering the conditioned flocculated tailings material.149. The method of claim 148, wherein removing air comprises reducing aviscosity of the flocculant solution sufficient to promote airliberation.
 150. The method of claim 149, further comprising mixing theflocculant solution after reducing the viscosity thereof in order tofurther promote air liberation.
 151. The method of claim 148, whereinremoving air from the flocculant solution comprises venting theflocculant solution.
 152. The method of claim 150, wherein the entrainedair in the flocculant solution comprises air present in a pipelinethrough which the flocculant solution is supplied prior to start-up; andair entrained during contacting of dry flocculant with water duringpreparation of the flocculant solution.
 153. A method for treating thickfine tailings, comprising: providing an in-line flow of the thick finetailings; adding a flocculant solution into the in-line flow of thethick fine tailings to produce an in-line flow of flocculating tailingsmaterial; shearing the in-line flow of the flocculating tailingsmaterial to produce an in-line flow of flocculated material; subjectingthe in-line flow of the flocculated material to shear conditioning toproduce a conditioned flocculated tailings material that is within awater release zone wherein water separates from the conditionedflocculated tailings material; dewatering the conditioned flocculatedtailings material; and removing air from the flocculant solution priorto adding the flocculant solution into the in-line flow of thick finetailings to thereby attenuate oscillations in a flow rate of theflocculant solution.
 154. The method of claim 153, further comprising:pumping the thick fine tailings using a first pump; controlling thefirst pump based on a flow rate set point of the thick fine tailings;pumping the flocculant solution using a second pump; controlling thesecond pump based on a flow rate set point of the flocculant solution;and regulating the flow rate set point of the flocculant solution basedon flow rate, density and/or clay content of the thick fine tailings.155. The method of claim 154, wherein the first and second pumps havefixed rotations per minute (RPM), and wherein controlling the flocculantdosage is performed based on pre-determined optimal flocculant dosage